The PW Arms Magazine System (100 round drum) is incompatible with the SCAR. The shape of the "feed clip" forces the bolt hold open device to remain engaged when the magazine is in the well (you cannot operate the release), and the shape of the back of the "feed clip" will block the moving parts group from advancing.

The troy battle mags are great as well as the D&H mags as they are the current manufacturer for FN. You can also use PMAGS with some modifications as I have 7 of them. You can also use the EMAGS without modifications.